I'm with you, daagh - this may have been a fair GMAT question in the 1980s when it was overwhelmingly an American test competing with the GRE and its vocabulary emphasis, but the GMAT has evolved to a point at which this isn't a relevant question.
Stationary (standing still) vs. stationery (paper for writing)
and
Snuck vs. Sneaked
...just aren't relevant comparisons of pre-MBAs from around the world, many of whom have learned different dialects of English (British vs. American vs. Australian). The GMAT is interested in your problem solving skills and capacity to be efficient; this question doesn't give an opportunity to test either, instead focusing on (as daagh demonstrated) fairly obscure and even subjective knowledge of minor linguistic subtleties.
Please do worry about (eh, not worry about - focus on) big-picture error types like Verb Tense, Subject-Verb Agreement, etc. But even for those of us who have been speaking English for 30 years, the little idiomatic subtleties are hard to pin down, so they don't make for good pre-MBA differentiation and aren't going to be a great use of your study time.